Electrical-including radio-apparatus



15, 1933. 1 M, BANK ELECFRICAL-INCLUDINGRADIO-APPARATUS Filed March '25,1929- MA U/P/CE BAN/f I v 5... I'll Invenfor Patented Aug. 15, 1933UNITED STATES PATENTWOFFICE ELECTRICAL-INCLUDING memo-APPARATUS Thisinvention relates to electrical apparatusincluding radioin general. 1

It is highly desirable in many institutions to have a system ofloud-speaking communication involving a central station and remotestations and in which the central station may communicate with theremote stations and vice-versa, and the various stations may receivecommunications, jointly or severally, eminating from an outside source.It is furthermore highly de-- sirable that such a system involve aminimum of apparatus and be as simple as possible.

Heretofore such a system has not been practicable because of thedifficulty in rendering sufliciently effective the slight fluctuationsof current in a reproducer circuit resulting from sound waves actingupon the reproducer whereby these fluctuations -may cause thereproduction of the sound in another reproducer in the circuit. Byproperly avoiding-unnecessary capacities I am enabled to provide such asystem utilizing a minimum of amplification and simple switchingapparatus.

It is accordingly the primary-object of this invention to provide such asystem in which a plurality of loud speaking reproducers are used atrespective stations and are so united that either one may be selectivelyused as either a transmitter or a reproducer to transmit to or receivefrom another.

Another object of this invention is to provide a system of the abovetype which includes means whereby a plurality of stations may eitherjointly or severally be controlled to selectively receive communicationsfrom a radio receiving set or a phonograph record.

A further object of this invention is .to provide a system ofcommunication involving a plurality of stations, each provided with aloud speaking reproducer capable of being used as a transmitter fortransmitting communications to 'a loud speaking reproducer at anotherstation thru the intermediary of a minimum of stages of amplification.

A still further object in this invention is-to provide a system ofcommunication involving a plurality of stations, each provided with aloud speaking reproducer and connections between these reproducershaving a minimum of capacity permitting the selectiveuse of onereproducer as a transmitter for transmitting communications to anotherreproducer.

Other and further objects of this invention will be apparent as the samebecomes better understood from an examination of the specification andclaims in connection with the accompanying drawing, wherein is shown adiagrammatic view of a system embodying this invention.

Referring to the drawing; more particularly, reference character 1indicates a loud speaking reproducer of the magnetictype situated in acentral station of a communication system. Nu-. merals 2 and 3 indicatesimilar loud speaking reproducers respectively, of remote stations,these reiraroducers being preferably arranged in para e At the centralstation wherein is located the reproducer 1 there is also located anamplification apparatus generally designated by the reference character4 including an audio-frequency transformer 5 adapted to receive theinput to the amplification apparatus and a vacuum tube 6 preferably apower amplifier tube, which with said transformer forms the first stageof amplification. A second audio-frequency transformer '7 and a secondvacuum tube 8- form the second stage of amplification. The second stageof amplification of apparatus 4 is connected to the input of a 1:1 ratiooutput coupling 9. In order that there may be a minimum of capacity inthe amplification apparatus and ultimately in the connections of thesystem between the reproducer- 1 and the reproducers 2 and 3 at the-remote stations, it, is highly essential to provide known negligiblecapacities 11 and 12 in the transformers 5 and 7 respectively and to usereproducers which do not require an external source of current. ,Inother words the input circuit to the amplification apparatus includingthe reproducers when the latter are used as transmitters should'notinclude an external source of current as would be the case were dynamictype loud speakers used asthis would result in indeterminate andinconstant inductances. By so eliminating indeterminate reactance in theconnec-' tions between the reproducers they are enabled to be usedefiiciently and selectively as transmitters.

A power supply terminal block 13 adapted to be energized by a suitableconnection (not shown) to an electric light socket (not shown) or othersource of power is provided with the terminals A, B, C, D, E, F and H.The terminal A has the'customary negative grid potential and isconnected to the secondary of the transformer 5. The terminal B is theusual negative power potential. The terminal C is the common negativefor the plate and filament circuits and the positive for the gridpotential. This terminal C is grounded. The'terminal D is the positivefor the filament circuits. The terminal E has no connection with theamplifier circuit, but provides the potential for a detector circuit ofa radio receiver which may be used as will be explained hereinafter inconjunction with the amplifier apparatus 4 for permitting thereproduction of external communications by the reproducers 1, 2

and 3. The terminal F provides the potential for the plate circuit ofthe 1st stage of amplification,

and the terminal H provides a power potential for the plate circuit ofthe output stage. I

The specific voltage of the various terminals is dependent upon therequirements of the power amplifier tubes 6 and 8.

When it is desired to use the loud speaking reproducer 1 as atransmitter for transmitting communications to the reproducers 2 and 3the input of the amplifier apparatus 4 is connected to said reproducer 1and the output of said apparatus is connected with the said reproducers2 and 3. When it is desired to use either of the reproducers 2 and 3 astransmitters for transmitting communications to the reproducer 1 forreproduction thereby at the central station the input of the amplifierapparatus 4 is connected to said reproducers 2 and 3 as the case may beand the output of said apparatus is connected to said reproducer 1. Theswitching of the input of the amplifier apparatus 4 from the reproducer1 to the reproducers 2 and 3 or vice versa and the switching of theoutput of said apparatus from the reproducers 2 and 3 to the reproducer1 or vice versa is accomplished by means of a non-capacity pole changerswitch 14 in circuit with said apparatus and reproducers as shown in thedrawing. 7

There is also employed in the circuit with the reproducers and theswitch 14 a radio receiving apparatus 15 and a phonograph record pick-up16, and it is therefore necessary to employ in addition to the switch 14a non-capacity double pole double throw switch 17 and a four pole doublethrow jack switch 18 as shown in the drawing for permittingcommunications from said receiver or pickup to be reproduced by thereproducers when it is not desired to use the latter forintercommum'cation. The switches 14 and 17 include input connections tothe amplifier apparatus 4 and consequently it is essential that they benon-capacity switches in order that the fluctuations of the inputcircuit to the amplifier apparatus caused by the respective reproducerswhen they are used as transmitters, may have a maximum of eifectiveness.To further enhance the effectiveness of the fluctuations caused by thereproducers in the remote stations when used as transmitters the leadsthereto are twisted as shown, thereby eliminating inductance. Thevarious parts of the circuit are shielded as indicated by the dottedlines 10 to further prevent interference with the fluctuations caused bythe reproducers when the same are used as transmitters. These shields 10are grounded to a common ground.

The non-capacity switch 18 is so connected that it may be selectivelyactuated to connect the input of the amplifier apparatus 4 with eitherthe output of radio receiving apparatus 15 or the reproducers 1, 2 and 3thru the intermediary of the switches 14 and 18.

The switches 14 and 18 are so connected that the latter when in oneposition may connect the reproducers thru the intermediary of the formerand the switch 17 with the input of the amplifier apparatus 4. Theswitches 14 and 18 are so connected that the latter when in downwardly(viewtween this switch 18 and the input to the amplifier apparatus 4.

The circuits from the reproducers which pass from the switch 18 to theswitch 14 are so arranged with respect to the latter that the same isenabled to render any capacity negligible which may have been built upin the circuit between said switch 14 and reproducers.

In this regard the outer contacts on the switch 1.4 are connected to thecommon terminal A and thus grounded thru the grid potential of theamplifier apparatus, so as to reduce any capacity which might otherwisebe built up in the switch. Such a capacity is further reduced in theswitch 14 by the arrangement whereby the two center blades 19 and 21 areconnected respectively to one leg of the opposing reproducer circuitsand these blades are adapted to selectively contact a center contact 22on the switch which is connected to the input of the amplifier circuitthru the intermediary of switch 17. By this arrangement oppositecircuits are at all times disposed ad:

jacent to each other in the switch 14 and in addition a comparativelyshort lead from the switch to the input of the amplifier apparatusresults whereby capacity other than that specifically provided for ispractically eliminated in the circuit.

The record pick-up 16 which in this instance is of the variable magnetictype is adapted to be connected to the input of the amplifier apparatus4 thru the intermediary of a single pole switch 23 and the previouslymentioned switch 17. The switch 23 should be opened when the pick-up 16is not being used so as to prevent heavy currents being fed back to thepick-up when the reproducers are being used in inter-communication toprevent capacity losses being built up when the reproducers are being soused and also saturating the magnet in the pick-up.

A pair of single pole switches 24 and 25 and connections as shownbetween the switch 18 and the output of the amplifier apparatus 4 areprovidcd whereby when said switch 18 is in upwardly closed position thereproducers are connected to the output of the amplifier apparatus forthe reception of radio or record communications and the central stationreproducer 1 or the remote station reproducers 2 and'3 maybe cut out asdesired.

In the operation of the afore-described ap paratus when it is desired touse the reproducers for inter-communication the switch 17 is actuated tothe down position shown; the switch 18 is actuated to the down positionshown and the switch 14 is selectively actuated to the up position shownassuming it is desired to talk from the central station to the remotestations or the latter switch may be actuated to its down position shownin dotted lines if it is desired to talk from any of the remote stationsto central station. It is important, however, when so using thereproducers to first open the switch 23 to prevent the capacity lossesbeing built up by the feeding back of currents to the pick-up 16 aspreviously described. All of these switches being located at the centralstation preferably in panel form, the entire control is at the will ofthe operator at said station.

When it is desired that phonograph record communications be received atthe various stations, switch 18 is actuated to its upper position toconnect the reproducers to the output of the amplifier apparatus andswitch 23 is closed. This movement of switch 18 entirely disconnectsswitch 14 from the circuit. Should it be desired to-eliminate either thereproducer 1 at central station or the reproducers 2 and'3 at the remotestation from the reception, switch 24 or 25 respectively may be opened.(It will be noted that when the switch 18 is in the down position shown,the switches 24 and 25 are out of the circuit.)

When it is desired that radio communications be received at the variousstations, the switch 17 is actuated to its upwardly closed position toconnect the output of the radio receiver 15 to the input of theamplifier apparatus 4 whereby, when the switch 18 is in its downwardlyclosed position, the output of the amplifier apparatus 4 will deliverthe amplified communications to either the central station reproducer 1or the outlying reproducers, depending upon the position of the switch14. If the switch 18 is in its upwardly closed position, and theswitches 24 and 25 are both closed, the radio-communication will bereceived at the reproducers in both the central station and the remotestations.

The efficiency of the afore-described apparatus is dependent upon theelimination of indeterminate inductance and more particularly capacitiesin the input circuit to the amplifier apparatus and the stages ofamplification therein. This elimination of indeterminate inductances andcapacities is accomplished as previously described by the use of theparticular form of reproducers, switches and circuits described, and theuse of predetermined capacities in the circuits in general and moreparticularly between the primary and secondary of the transformers inthe amplifier apparatus. The elimination of indeterminate inductances isfurther provided for by the use of the twisted wire leads to the remotestation reproducers. A condenser 20 of predetermined negligible capacityis provided across the record pick-up to further prevent the building upof undesired capacities.

It will be apparent that the system will be very useful in institutionsboth for interior communication and for the reception of externalcommunications as from a radio receiver or a phonograph record.

I am aware that many changes may be made without departingfrom theprinciples of my invention, and I, therefore, do not wish to be limitedto the details shown or described.

I claim: 1

1. In an apparatus of the character described, the combination of aplurality of loud speaking reproducers in circuit and anamplificationapparatus in said circuit adapted to receive inputfluctuations from one reproducer and deliver amplified fluctuations toanother, said amplification apparatus including fication stage providedwith a predetermined capacity for preventing the building up of a capacity between the primary and secondary of said transformer and forpermitting the emcient operation of said reproducer as a transmitter.

2. In an apparatus of the character described,

the combination of a plurality of loud speaking reproducers in circuitand means associated with said circuit including a r'nulti-pole switchwhereby one reproducer may be selectively used to transmit-to as well asreceive from another reproducerand vice versa, connected that itsadjacent blades are connected to separate reproducers whereby thecapacity that wouldotherwise be built up in said switch is reduced. v p

3. In an apparatus of the character described, the combination of aplurality of loud speaking reproducers in circuit, and a multi-poleswitch so connected with respect to said reproducers and means that itmay be actuated to selectively connect one reproducer to the input ofsaid means and another a transformer in an ampli-- said switch being so7 circuit, amplifier means in said 1 reproducer to the output thereofand vice versa,

the circuit is reduced. I

MAURICE BANK.

